Instant-on filament circuit

ABSTRACT

A solid-state television receiver includes a cathode ray tube having a heater filament coupled to the secondary winding of a filament transformer having a gap in the magnetic core. The primary winding of the filament transformer is coupled through a first diode and a low value resistor to an AC source in order to continuously preheat the CRT filament with half-wave power. A single pole switch and a second diode shunt the first diode and the low value resistor to pass, when the switch is closed, fullwave power to the CRT filament and to energize a one-half wave power supply. The second diode is poled to block the inductive voltage surge generated by the filament transformer.

Worster INSTANT-ON FILAMENT CIRCUIT [75] Inventor: Frederick Ernest Worster, Highland Park, 111.

173} Assignee: Warwick Electronics Inc., Chicago,

[22] Filed: Nov. 23, 1973 121] App]. No.: 418,576

152] US. Cl 315/380; 315/20 [51] Int. Cl. H0lj 29/70 1158] Field of Search 315/20, 27 TD, 27 R, 28-29, 315/101, 380

[56] References Cited UNITED STATES PATENTS 3.462.640 8/1969 Eltgroth 315/20 3.535.445 10/1970 Griffery 3.801.856 4/1974 Griepentrog 315/20 55$?! AVAILABLE GDPY Primary Examiner-Maynard R. Wilbur Assistant E.\'aminer.l. M. Potenza Attorney, Agent, or FirmHofgren, Wegner, Allen, Stellman & McCord [57] ABSTRACT A solid-state television receiver includes a cathode ray tube having a heater filament coupled to the secondary winding of a filament transformer having a gap in the magnetic core. The primary winding of the filament transformer is coupled through a first diode and a low value resistor to an AC source in order to continuously preheat the CRT filament with half-wave power. A single pole switch and a second diode shunt the first diode and the low value resistor to pass, when the switch is closed, full-wave power to the CRT filament and to energize a one-half wave power supply. The second diode is poled to block the inductive voltage surge generated by the filament transformer.

PO WER SUPPLY I4 \fi 44 4O 24 27 0.4 28 i 3o ,5 L 37 L2 no v. AC II souncr: 36 4/ 26 INSTANT-ON FILAMENT CIRCUIT BACKGROUND OF THE INVENTION This invention relates to an instant-on type filament circuit for preheating a filament in order to eliminate warm-up time for an electrical apparatus such as a television receiver.

Instant-on circuits are used to preheat the filaments of a television receiver by continuously passing halfwave power to the filaments when the receiver is off" and a full-wave power when the receiver is turned on". For example, a single diode located to pass half wave power to tube filaments may be bypassed by a single pole switch when full-wave power is to be passed to the tube filaments and to energize a one-half wave power supply. An example of such a circuit is U.S. Pat. No. 3.339.105 to Busse. It is also known to preheat the filament of a cathode ray tube (CRT), such as shown in US. Pat. No. 3.5l4,532 to Ludham.

Often it is desirable to use a filament transformer for supplying power to a CRT heater filament. Unfortunately. a filament transformer when operated continuously at one-half wave power generates excessive heat. Also troublesome is the inductance of the filament transformer which produces an undesirable inductive voltage surge when the AC voltage changes polarity, since such an inductive surge can energize a half-wave power supply connected in parallel with the instant-on circuit. While the inductive voltage surge problem could be eliminated by use of multiple ganged switches, it is desirable that the master on-off switch be as simple as possible. such as a single pole, single throw (SPST) type switch, in order to reduce the number of components which are required. This is especially advantageous when the master control switch is to be implemented by a controlled rectifier, as occurs in a remote controlled receiver.

SUMMARY OF THE INVENTION ln accordance with the present invention, the problems with prior instant-on heating circuits have been eliminated. A CRT heater filament is supplied from a filament transformer having a gap in the magnetic core, which gap is selected to prevent excessive build-up of heat while the CRT filament is operated at reduced power. The problem of inductive voltage surge is eliminated by using a pair of diodes connected so that one diode continuously passes half-wave power to the CRT filament. and the other diode when enabled passes the remaining half-wave and also blocks the inductive voltage surge. The circuit uses a single pole, single throw type switch and a minimum number of components.

One object of the present invention is an improved instant-on circuit which uses a cool-running filament transformer and a minimum number of components.

Other objects and features of the invention will be apparent from the following description and from the drawing. While an illustrative embodiment of the invention is shown in the drawing and will be described in detail herein, the invention is susceptible of embodiment in many different forms and it should be understood that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a schematic diagram of the instant-on filament circuit as utilized in a solid-state television receiver.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to the single FIGURE, a cathode ray tube (CRT) 10 in a solid-state television receiver has a heater filament 11 forming a first utilization device which must be preheated in order to allow an instanton operation upon closure of a master control switch 14 for the television receiver, formed by a single pole, single throw (SPST) type switch. When the television receiver is to be remotely controlled. the SPST switch 14 would be implemented by a controlled rectifier such as an SCR. One terminal of the switch 14 is coupled by a line 15 directly to one side of the conventional AC voltage source 15, having a voltage such as volts. The opposite side of the AC source 16 is coupled to a reference line 17 which may serve as a chassis ground. The solid-state television receiver also includes a second utilization device in the form of a conventional one-half wave power supply 20 which includes a diode 21 poled to pass half-wave power to a filtering circuit. When positive polarity voltage is coupled to the anode of diode 21, the one-half wave power supply 20 is enabled and generates DC voltage for operating the television receiver.

In accordance with the present invention, the novel instant-on switching circuit includes a CRT filament transformer 24 which comprises an E-shaped magnetizable core section 26 having two outer legs and a center leg spaced from a rectangular core section 27. An insulating material 28 is placed between the legs of core 26 and the rectangular core 27 so as to define therebetween a gap 30 having a dimension such as 0.005 inches.

The filament transformer 24 has a primary winding 32, which forms a reactive impedance, wound about the center leg of core 26, and a secondary winding 34 which is also wound about the center leg of core 26. The turns ratio is conventional, and is selected to cause the filament transformer to step-down the voltage to an appropriate value for the CRT heater filament ll. Unlike a conventional CRT filament transformer which has no gap, the transformer 24 has a gap 30 which ensures that the core will not be saturated during standby operation and equalizes the temperature between standby and normal operation.

One side of the primary winding 32 is coupled through a line 36 to the reference line 17, and the other side of the primary winding 32 is coupled through a line 37 to a junction between the anode of a first diode 40 and the cathode of a second diode 42. The cathode of diode 40 is coupled to a resistor 44 of small resistance value, the opposite side of which is coupled to line 15. Diode 42 has its anode coupled to the line 19 which connects the anode of diode 21 of the one-half wave power supply 20 to the switching terminal of of switch 14.

When the television receiver is off, one-half wave power is passed through diode 40 to the primary winding 32. The resistor 44 serves as a limiting resistor to adjust the stand-by CRT heater voltage and can be kept to a small resistance value due to the operating point of the filament transformer 24 during standby operation. N path for energizing the one-half wave power supply is present during this stand'by condition.

When the television receiver is to be enabled for operation, switch 14 is closed. This causes power to flow through lines 17 and 19 to energize the one-half wave power supply 20. and also causes full-wave power to be coupled to the primary winding 32. As AC source 16 goes negative relative to line 17. power is passed through the primary winding 32 and the series combination of diode 40 and resistor 44. On the opposite half-cycle, power passes through switch 14 and diode 42 to the primary winding 32 and then returns via lines 36 and 17 to the AC source 16.

During stand-by, diode 42 blocks the inductive voltage surge, produced when the AC power switches polarity, from continuing to flow in a direction which could energize the one-half wave power supply 20. If for example, diode 42 was replaced with a short circuit, the inductive voltage surge at the end of the half-cycle during which current flowed through diode 40 would continue to flow in a direction which would pass through the diode and thus enable the one-half wave power supply 20. Diode 42 eliminates this problem. Also, the resistor 44 receives less average current over the full AC cycle because the inductive voltage surge from primary 32 is bucked by the alternating voltage passed by diode 42.

The gap in the filament transformer 24 serves to prevent excessive heat from building up while the filament transformer is operated at one-half power. The gap may be empirically chosen to tend to equalize the temperature between the stand-by and normal operation of the television receiver. The gap allows only par tial saturation of the core, and thereby serves to lower the temperature of the filament transformer during the stand-by mode.

Having described the invention, the embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A power supply for passing one-half wave power from an AC source to a filament during a stand-by mode and for passing full-wave power to the filament during an operating mode, comprising:

a filament transformer having a primary winding, and

a secondary winding coupled to the filament, each winding being wound on a magnetic core having a a diode,

a first circuit connecting said diode and the primary winding of the filament transformer to the AC source for passing one-half wave power from the AC source to the primary winding in order to partially energize the filament during the stand-by mode.

a switch, and

a second circuit enabled by the switch for passing full-wave power from the AC source to the primary winding in order to fully energize the filament during the operating mode.

2. The power supply of claim I wherein said filament transformer comprises a first core section having a plurality of legs, a second core section spaced from the legs of the first core section and defining therebetween the gap, at lease one of said windings being wound on one of said plurality of legs.

3. The power supply of claim 2 wherein said first core section comprises an E-shaped core having a pair of outer legs and a center leg, an insulating layer located between said legs and the second core section, said primary and said secondary windings being wound on said center leg.

4. The power supply of claim 1 wherein said second circuit includes a second diode located in series with said switch, said second diode being poled to block an inductive voltage surge produced by said primary wind- 5. The power supply of claim 4 including a one-half wave power supply having a third diode, said second diode being located between said primary winding and said one-half wave power supply and poled opposite to the third diode.

6. The power supply of claim 1 for a television receiver in which said filament forms a heater filament for a cathode ray tube.

7. An instant-on power supply for passing one-half wave power from an AC source to a first utilization device during a stand-by mode and for passing fullwave power to the first utilization device during an operating mode, comprising:

a first diode,

a reactive impedance,

a first circuit connecting said first diode and said reactive impedance between said AC source and said first utilization device to energize said first utilization device by one-half wave power passed through said first diode, said reactive impedance undesirably producing a voltage surge when the polarity of the AC voltage changes from said AC source,

a switch,

a second diode,

a second utilization device, and

a second circuit connecting said switch and said second diode with the first circuit to pass enabling power to the second utilization device when the switch is actuated, said second diode being poled to block the voltage surge from being passed to said second utilization device.

8. The power supply of claim 7 wherein said switch comprises a single pole, single throw type switch, and said second circuit connects with single pole, single throw type switch in series with said second diode.

9. The power supply of claim 7 wherein second utilization device comprises a one-half power supply having a third diode, said second diode being poled opposite to said third diode.

10. The power supply of claim 7 including a resistor, said first circuit connecting the first diode and said resistor in series between said AC source and said first utilization device.

11. The power supply of claim 7 wherein said first utilization device comprises a heater filament, a filament transformer having a primary winding and a secondary winding coupled to said heater filament, and said primary winding being connected to both said first and second circuits.

12. The power supply of claim 11 wherein said filament transformer comprises a first core section and a second core section spaced therefrom to form a gap therebetween, said primary and secondary windings being wound about one core section. 

1. A power supply for passing one-half wave power from an AC source to a filament during a stand-by mode and for passing fullwave power to the filament during an operating mode, comprising: a filament transformer having a primary winding, and a secondary winding coupled to the filament, each winding being wound on a magnetic core having a gap, a diode, a first circuit connecting said diode and the primary winding of the filament transformer to the AC source for passing one-half wave power from the AC source to the primary winding in order to partially energize the filament during the stand-by mode, a switch, and a second circuit enabled by the switch for passing full-wave power from the AC source to the primary winding in order to fully energize the filament during the operating mode.
 2. The power supply of claim 1 wherein said filament transformer comprises a first core section having a plurality of legs, a second core section spaced from the legs of the first core section and defining therebetween the gap, at lease one of said windings being wound on one of said plurality of legs.
 3. The power supply of claim 2 wherein said first core section comprises an E-shaped core having a pair of outer legs and a center leg, an insulating layer located between said legs and the second core section, said primary and said secondary windings being wound on said center leg.
 4. The power supply of claim 1 wherein said second circuit includes a second diode located in series with said switch, said second diode being poled to block an inductive voltage surge produced by said primary winding.
 5. The power supply of claim 4 including a one-half wave power supply having a third diode, said second diode being located between said primary winding and said one-half wave power supply and poled opposite to the third diode.
 6. The power supply of claim 1 for a television receiver in which said filament forms a heater filament for a cathode ray tube.
 7. An instant-on power supply for passing one-half wave power from an AC source to a first utilization device during a stand-by mode and for passing full-wave power to the first utilization device during an operating mode, comprising: a first diOde, a reactive impedance, a first circuit connecting said first diode and said reactive impedance between said AC source and said first utilization device to energize said first utilization device by one-half wave power passed through said first diode, said reactive impedance undesirably producing a voltage surge when the polarity of the AC voltage changes from said AC source, a switch, a second diode, a second utilization device, and a second circuit connecting said switch and said second diode with the first circuit to pass enabling power to the second utilization device when the switch is actuated, said second diode being poled to block the voltage surge from being passed to said second utilization device.
 8. The power supply of claim 7 wherein said switch comprises a single pole, single throw type switch, and said second circuit connects with single pole, single throw type switch in series with said second diode.
 9. The power supply of claim 7 wherein second utilization device comprises a one-half power supply having a third diode, said second diode being poled opposite to said third diode.
 10. The power supply of claim 7 including a resistor, said first circuit connecting the first diode and said resistor in series between said AC source and said first utilization device.
 11. The power supply of claim 7 wherein said first utilization device comprises a heater filament, a filament transformer having a primary winding and a secondary winding coupled to said heater filament, and said primary winding being connected to both said first and second circuits.
 12. The power supply of claim 11 wherein said filament transformer comprises a first core section and a second core section spaced therefrom to form a gap therebetween, said primary and secondary windings being wound about one core section. 